Impression Creep of a Lead-Free Sn-1.7Sb-1.5Ag Solder Reinforced by Submicron-Size Al₂O₃ Particles

Abstract

In the present study, the Sn-1.7Sb-1.5Ag solder alloy and the same material reinforced with 5 vol.% of 0.3-μm Al₂O₃ particles were synthesized using the powder metallurgy route of blending, compaction, sintering, and extrusion. The impression creep behavior of both monolithic and composite solders was studied under a constant punching stress in the range of 20 MPa to 110 MPa, at temperatures in the range of 320 K to 430 K. The creep resistance of the composite solder was higher than that of the monolithic alloy at all applied stresses and temperatures, as indicated by their corresponding minimum creep rates. This was attributed to the dispersive distribution of the submicron-sized Al₂O₃ particles in the composite solder. Assuming a power-law relationship between the impression stress and velocity, average stress exponents of 5.3 to 5.6 and 5.8 to 5.9 were obtained for the monolithic and composite materials, respectively. Analysis of the data showed that, for all loads and temperatures, the activation energy for both materials was almost stress independent, with average values of 44.0 kJ mol⁻¹ and 41.6 kJ mol⁻¹ for the monolithic and composite solders, respectively. These activation energies are close to the value of 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about 5 to 5.9, suggests that the operative creep mechanism is dislocation viscous glide controlled by dislocation pipe diffusion.